Accept source attributes in PaymentsController to fix backend payment processing.
Add process method to BogusSimple gateway to be able to process payments.

Fixes issue where hitting "process" on payments screen breaks with
BogusSimple gateway.
[backend] Remove unnecessary top-level admin route for adjustments
Account for adjustments with nil sources in UpgradeAdjustments migration
Skip PromotionAction adjustments if originator is nil